This invention is related to the fueling of internal combustion engines with alcohol-gasoline mixtures, and more particularly, to an apparatus for discriminating between different types of alcohol, such as ethanol or methanol, contained in an alcohol-gasoline fuel mixture and a system for controlling the quantity of such a fuel delivered to an engine based upon the type of alcohol determined to be present in the fuel mixture.
To conserve oil reserves and reduce air pollution, alcohols such as ethanol and methanol are being proposed as possible alternatives to gasoline for fueling internal combustion engines. Although it is possible to operate an engine on a pure alcohol fuel, gasoline is generally blended with a particular alcohol to increase the vapor pressure of the fuel mixture to improve engine cold starting and warm-up operation.
It is well known that engines running on blended alcohol-gasoline fuels must be operated at stoichiometric air/fuel ratios depending upon on the relative proportions of the particular alcohol and gasoline in the fuel mixtures for optimal combustion. For warmed-up engine operation, this is generally accomplished by sensing the composition of the fuel mixture to determine the proper stoichiometric air/fuel ratio, and then regulating the delivery of fuel to the engine using conventional closed-loop computer control to achieve operation at the determined stoichiometric air/fuel ratio (see for example U.S. Pat. No. 4,915,084 issued to Gonze on Apr. 10, 1990).
Due to the low volatility of ethanol and methanol, the fraction of gasoline in an alcohol-gasoline mixture provides most of the combustible vapor when the engine is started, and first operated at low ambient temperatures. Consequently, engines operated on fuel mixtures having high alcohol concentrations are usually difficult to start at low temperatures, and vehicles employing such engines typically exhibit poor driveability during the engine warm-up period. The conventional approach to solving these problems has been to appropriately increase the amount of the fuel delivered to an engine during these operating periods, in accordance with the relative proportion of the particular alcohol to gasoline in the fuel mixture, to assure that a sufficient amount of gasoline vapor is present for combustion.
The problem with this approach is that conventional engine control computers are calibrated or programmed for operation with either variable ethanol-gasoline fuel mixtures or variable methanol-gasoline fuel mixtures. Hence, the type of alcohol to be used in the blended fuel mixture must be known apriori for proper fuel regulation during cold starting and engine warm-up. Once an engine control system is calibrated for a particular type of alcohol-gasoline mixture, engine cold starting and warm-up performance will generally be degraded if the engine is then operated with a fuel blend containing a different type of alcohol. This occurs because alcohol such as ethanol and methanol have different properties, and conventional fuel composition sensors calibrated for use with one type of alcohol will not indicate the correct fraction of gasoline in the fuel mixture, when another type alcohol is used in the fuel mixture to operate the engine. As a result, the fuel mixture delivered to an engine, when the closed-loop fuel control is not operable (during cold starting and warm-up), will generally be either too rich or too lean, and the engine cold starting and warm-up performance will be degraded.
Consequently, there exists a need for an apparatus capable of discriminating between alcohols such as ethanol or methanol contained in an alcohol-gasoline fuel mixture, and for a fuel control system capable of adjusting the quantity of fuel delivered to an engine based upon the type of alcohol determined to be present in the fuel mixture so the engine can be operated with different types of alcohol-gasoline fuel mixtures without degrading engine cold starting and warm-up performance.